Liquid-crystal display devices are widely used as display devices for televisions, personal computers, and PDAs because these have a thin profile, a light weight, and low power consumption. Particularly, recently, enlarging of the size of the liquid-crystal display device has been rapidly progressed as shown in liquid-crystal display devices for television, for example. For the enlarging of the size, a vertical alignment mode (VA) is suitably used in which a liquid-crystal display device having a large area can be produced at a higher yield, and a wide viewing angle is provided. In the vertical alignment mode, when no voltage is applied within a liquid crystal layer, liquid crystal molecules are aligned orthogonal to the surface of a substrate. Thereby, a high contrast ratio can be obtained.
As an example of application of the vertical alignment mode, for example, a method is disclosed in which a protrusion (rib) is formed in a surface facing a liquid crystal layer to give a pretilt angle to liquid crystal molecules in the vicinity of the rib, and voltage is applied to control the orientation of the liquid crystal molecules when the liquid crystal molecules are horizontally aligned to secure a wide viewing angle (for example, see Patent Literature 1.). Other method is known in which a slit is provided in a display electrode to generate an inclined electric field region, thereby to control the horizontal alignment orientation of liquid crystal molecules (for example, see Non-Patent Literature 1.).
Unfortunately, the method using the rib or the electrode slit is susceptible to improvement because not the whole surface of pixels is subjected to the pretilt aligning treatment, most of the pixel region has the pretilt angle of 90°, and the response time is slow. Then, a method is disclosed in which an alignment film is rubbed in four directions to divide pixels into four domains; thereby, the pretilt angle of liquid crystal molecules in a whole pixel region is approximately 88° (for example, see Patent Literature 2.). Other method is disclosed in which an alignment division is performed by a photoalignment method to give substantially the same pretilt angle as that in the method above to liquid crystal molecules (for example, see Patent Literature 3.).
Thereby, the pretilt angle can be given to the liquid crystal molecules in the whole pixel region to improve the response time. Unfortunately, in these methods, display of the same pattern for a long time may cause “image sticking” in the display. As a countermeasure, a method for suppressing occurrence of image sticking is disclosed in which an alignment film is formed using a polymer material including a side chain including a predetermined or more weight average molecular weight to the molecular weight of liquid crystal molecules (for example, see Patent Literature 4.).